Control system for a furfural refining unit receiving medium sweet charge oil

ABSTRACT

A furfural refining unit treates medium sweet charge oil with a furfural solvent in a refining tower to yield raffinate and extract mix. The furfural is recovered from the raffinate and from the extract mix and returned to the refining tower. A system controlling the refining unit includes a gravity analyzer, a refractometer and viscosity analyzer, all analyzing the medium sweet charge oil and providing corresponding signals, sensors sense the flow rates of the charge oil and the furfural flowing into the refining tower and the temperature of the extract mix and provide corresponding signals. One of the flow rates of the medium sweet charge oil and the furfural flow rates is controlled in accordance with the signals from all the analyzers and all the sensors, while the other flow rate of the medium sweet charge oil and the furfural flow rates is constant.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation as to all subject matter common to U.S. application Ser. No. 851,995 filed Nov. 16, 1977, now abandoned, by Avilino Sequeira, Jr. John D. Begnaud and Frank L. Barger and assigned to Texaco Inc., assignee of the present invention, and a continuation in-part for additional subject matter.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to control systems and methods in general and, more particularly, to control systems and methods for oil refining units.

SUMMARY OF THE INVENTION

A furfural refining unit treats medium sweet charge oil with a furfural solvent in a refining tower to yield raffinate and extract mix. The furfural is recovered from the raffinate and from the extract mix and returned to the refining tower. A system controlling the refining unit includes a gravity analyzer, a flash point temperature analyzer, a sulfur analyzer, a refractometer and viscosity analyzers. The analyzers analyze the medium sweet charge oil and provide corresponding signals. Sensors sense the flow rates of the charge oil and the furfural flowing into the refining tower and the temperature of the extract-mix and provide corresponding signals. The flow rate of the medium sweet charge oil or the furfural is controlled in accordance with the signals provided by all the sensors and the analyzers while the other flow rate of the medium sweet charge oil or the furfural is constant.

The objects and advantages of the invention will appear more fully hereinafter from a consideration of the detailed description which follows, taken together with the accompanying drawings wherein one embodiment of the invention is illustrated by way of example. It is to be expressly understood, however, that the drawings are for illustration purposes only and are not to be construed as defining the limits of the invention.

DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a furfural refining unit in partial schematic form and a control system, constructed in accordance with the present invention, in simple block diagram form.

FIG. 2 is a detailed block diagram of the control means shown in FIG. 1.

FIGS. 3 through 14 are detailed block diagrams of the H computer, the K signal means, the H signal means, the KV computer, the VI signal means, the SUS computer, the SUS₂₁₀ computer, the W computer, the VI_(DWC).sbsb.O computer, the VI_(DWC).sbsb.P computer, the A computer and the J computer, respectively, shown in FIG. 2.

DESCRIPTION OF THE INVENTION

An extractor 1 in a furfural refining unit is receiving medium sweet charge oil by way of a line 4 and furfural solvent by way of a line 7 and providing raffinate to recovery by way of a line 10, and an extract mix to recovery by way of a line 14.

Medium sweet charge oil is a charge oil having a sulfur content equal to or less than a predetermined sulfur content and having a kinematic viscosity, corrected to a predetermined temperature, less than a first predetermined kinematic viscosity but equal to or less than a second predetermined kinematic viscosity. Preferable, the predetermined sulfur content is 1.0%, the predetermined temperature is 210° F., and the first and second predetermined kinematic viscosities are 7.0 and 15.0, respectively. The temperature in extractor 1 is controlled by cooling water passing through a line 16. A gravity analyzer 20, flash point analyzer 22 and viscosity analyzers 23 and 24, a refractometer 26 and a sulfur analyzer 28 sample the charge oil in line 4 and provide signals API, FL, KV₂₁₀, KV₁₅₀ and S, respectively, corresponding to the API gravity, the flash point, the kinematic viscosities at 210° F. & 150° F., the refraction index and sulfur content, respectively.

A flow transmitter 30 in line 4 provide a signal CHG corresponding to the flow rate of the charge oil in line 4. Another flow transmitter 33 in line 7 provides a signal SOLV corresponding to the furfural flow rate. A temperature sensor 38, sensing the temperature of the extract mix leaving extractor 1, provides a signal T corresponding to the sensed temperature. All signals hereinbefore mentioned are provided to control means 40.

Control means 40 provides signal C to a flow recorder controller 43. Recorder controller 43 receives signals CHG and C and provides a signal to a valve 48 to control the flow rate of the charge oil in line 4 in accordance with signals CHG and C so that the charge oil assumes a desired flow rate. Signal T is also provided to temperature controller 50. Temperature controller 50 provides a signal to a valve 51 to control the amount of cooling water entering extractor 1 and hence the temperature of the extract-mix in accordance with its set point position and signal T.

The following equations are used in practicing the present invention for medium sweet charge oil:

    H.sub.210 =lnln(KV.sub.210 +C.sub.1)                       1.

where H₂₁₀ is a viscosity H value for 210° F., KV₂₁₀ is the kinematic viscosity of the charge oil at 210° F. and C₁ is a constant having a preferred value of 0.6.

    H.sub.150 =lnln(KV.sub.150 +C.sub.1)                       2.

where H₁₅₀ is a viscosity H value for 150° F., and KV₁₅₀ is the kinematic viscosity of the charge oil at 150° F.

    K.sub.150 =[C.sub.2 -ln(T.sub.150 +C.sub.3 ]/C.sub.4       3.

where K₁₅₀ is a constant needed for estimation of the kinematic viscosity at 100° F., T₁₅₀ is 150, and C₂ through C₄ are constants having preferred values of 6.5073, 460 and 0.17937, respectively.

    H.sub.100 =H.sub.210 +(H.sub.150 -H.sub.210)/K.sub.150     4.

where H₁₀₀ is a viscosity H value for 100° F.

    kv.sub.100 =exp[exp(H.sub.100)]-C.sub.1                    5.

where KV₁₀₀ is the kinematic viscosity of the charge oil at 100° F.

    sus=c.sub.5 (kv.sub.210)+[c.sub.6 +c.sub.7 (kv.sub.210)]/[c.sub.8 +c.sub.9 (kv.sub.210)+c.sub.10 (kv.sub.210).sup.2 +c.sub.11 (kv.sub.210).sup.3 ](c.sub.12)                                               6.

where SUS is the viscosity in Saybolt Universal Seconds and C₅ through C₁₂ are constants having preferred values of 4.6324, 1.0, 0.03264, 3930.2, 262.7, 23.97, 1.646 and 10⁻⁵, respectively.

    SUS.sub.210 =[C.sub.13 +C.sub.14 (C.sub.15 -C.sub.16)]SUS  7.

where SUS₂₁₀ is the viscosity in Saybolt Universal Seconds at 210° F. and C₁₃ through C₁₆ are constants having preferred values of 1.0, 0.000061, 210 and 100, respectively.

    W=C.sub.43 -C.sub.45 API+C.sub.45 /KV.sub.210 -C.sub.46 S+C.sub.47 (API).sup.2 -C.sub.48 API/KV.sub.210 +C.sub.49 (S)(API),  8.

where W is the percent wax in the charge oil, and C₄₃ through C₄₉ are constants having preferred values of 51.17 4.3135, 182.83, 5.2388, 0.101, 6.6106 and 0.19609, respectively.

    VI.sub.DWC.sbsb.O =C.sub.50 -C.sub.51 RI+C.sub.52 (RI)(VI)+C.sub.53 (FL)(API)-C.sub.54 (W)(VI),                               9.

where C₅₀ through C₅₄ are constants having preferred values of 2306.54, 1601.786, 1.33706, 0.00945 and 0.20915, respectively.

    VI.sub.DWC.sbsb.P =VI.sub.DWC.sbsb.O +(Pour)[C.sub.21 -C.sub.22 lnSUS.sub.210 +C.sub.23 (InSUS.sub.210).sup.2 ]           10.

where VI_(DWC).sbsb.P and Pour are the viscosity index of the dewaxed product at a predetermined temperature and the Pour Point of the dewaxed product, respectively, and C₂₁ through C₂₃ are constants having preferred values of 2.856, 1.18 and 0.126, respectively.

    ΔVI=VI.sub.RO -V.sub.DWC.sbsb.O =VI.sub.RP -VI.sub.DWC.sbsb.P 11.

where VI_(RO) and VI_(RP) are the VI of the dewaxed refined oil at 0° F., and the predetermined temperature, respectively.

    A=C.sub.55 -C.sub.56 (API)+C.sub.57 (FL)(KV.sub.210),      12.

where C₅₅ through C₅₇ are constants having preferred values of 860.683, 28.9516 and 0.02389, respectively.

    J={{-C.sub.58 A+{(C.sub.58 A).sup.2 -4C.sub.59 A(C.sub.60 +C.sub.81 √T-ΔVI)}.sup.1/2 }/2C.sub.59 A}.sup.2        13.

where J is the furfural dosage and C₅₈ through C₆₁ are constants having preferred values of 0.013795, -0.00025376, -18.233 and 1.1031, respectively.

    C=(SOLV) (100)/J                                           14.

where C is the new charge oil flow rate.

Referring now to FIG. 2, signal KV₂₁₀ is provided to an H computer 50 in control means 40, while signal KV₁₅₀ is applied to an H computer 50A. It should be noted that elements having a number and a letter suffix are similar in construction and operation as to those elements having the sane numeric designation without a suffix. All elements in FIG. 2, except elements whose operation is obvious, will be disclosed in detail hereinafter. Computers 50 and 50A provide signals E₁ and E₂ corresponding to H₂₁₀ and H₁₅₀, respectively, in equations 1 and 2, respectively, to H signal means 53. K signal means 55 provides a signal E₃ corresponding to the term K₁₅₀ in equation 3 to H signal means 53. H signal means 53 provides a signal E₄ corresponding to the term H₁₀₀ in equation 4 to a KV computer 60 which provides a signal E₅ corresponding to term KV₁₀₀ in accordance with signal E₄ and equation 5 as hereinafter explained.

Signals E₅ and KV₂₁₀ are applied to VI signal means 63 which provides a signal E₆ corresponding to the viscosity index.

An SUS computer 65 receives signal KV₂₁₀ and provides a signal E₇ corresponding to the term SUS in accordance with the received signals and equation 6 as hereinafter explained.

An SUS 210 computer 68 receives signal E₇ and applies signal E₈ corresponding to the term SUS₂₁₀ in accordance with the received signal and equation 7 as hereinafter explained.

A W computer 69 receives signals KV₂₁₀, S and API and provides a signal E₉ corresponding to the term W in equation 8 in accordance with the received signals and equation 8 as hereinafter explained.

A VI_(DWC).sbsb.O computer 70 receives signals RI, E₉, API, FL and E₆ and provides a signal E₁₀ corresponding to the term VI_(DWC).sbsb.O in accordance with the received signals and equation 9 as hereinafter explained.

A VI_(DWC).sbsb.P computer 72 receives signal E₈ and E₁₀ and provides a signal E₁₁ corresponding to the term VI_(DWC).sbsb.P in accordance with the received signals and equation 10. Subtracting means 76 performs the function of equation 11 by subtracting signal E₁₁ from a direct current voltage V₉ corresponding to the term VI_(RP), in equation 11, to provide a signal E₁₂ corresponding to the term ΔVI in equation 11.

An A computer 79 receives signals KV₂₁₀, API and FL and provides a signal A corresponding to the term A in equation 12, in accordance with the received signals and equation 12 as hereinafter explained.

A J computer 80 receives signals T, E₁₁ and E₁₂ and provide a signal E₁₃ corresponding to the term J in accordance with the received signals and equation 12 as hereinafter explained to a divider 83.

Signal SOLV is provided to a multiplier 82 where it is multiplied by a direct current voltage V₂ corresponding to a value of 100 to provide a signal corresponding to the term (SOLV) (100) in equation 13. The product signal is applied to divider 83 where it is divided by signal E₁₃ to provide signal C corresponding to the desired new charge oil flow rate.

It would be obvious to one skilled in the art that if the charge oil flow rate was maintained constant and the furfural flow rate varied, equation 14 would be rewritten as

    SO=(J) (CHG)/100                                           15.

where SO is the new solvent flow rate. Control means 40 would be modified accordingly.

Referring now to FIG. 3, H computer 50 includes summing means 112 receiving signal KV₂₁₀ and summing it with a direct current voltage C₁ to provide a signal corresponding to the term [KV₂₁₀ +C₁ ] shown in equation 1. The signal from summing means 112 is applied to a natural logarithm function generator 113 which provides a signal corresponding to the natural log of the sum signal which is then applied to another natural log function generator 113A which in turn provides signal E₁.

Referring now to FIG. 4, K signal means 55 includes summing means 114 summing direct current voltage T₁₅₀ and C₃ to provide a signal corresponding to the term [T₁₅₀ +C₃ ] which is provided to a natural log function generator 113B which in turn provides a signal corresponding to the natural log of the sum signal from summing means 114. Subtracting means 115 subtracts the signal provided by function generator 113B from a direct current voltage C₂ to provide a signal corresponding to the numerator of equation 3. A divider 116 divides the signal from subtracting means 115 with a direct current voltage C₄ to provide signal E₃.

Referring now to FIG. 5, H signal means 53 includes subtracting means 117 which subtracts signal E₁ from signal E₂ to provide a signal, corresponding to the term H₁₅₀ -H₂₁₀, in equation 4, to a divider 118. Divider 118 divides the signal from subtracting means 117 by signal E₃. Divider 114 provides a signal which is summed with signal E₁ by summing means 119 to provide signal E₄ corresponding to H₁₀₀.

Referring now to FIG. 6, a direct current voltage V₃ is applied to a logarithmic amplifier 120 in KV computer 60. Direct current voltage V₃ corresponds to the mathematical constant e. The output from amplifier 120 is applied to a multiplier 122 where it is multiplied with signal E₄. The product signal from multiplier 122 is applied to an antilog circuit 125 which provides a signal corresponding to the term exp (H₁₀₀) in equation 5. The signal from circuit 125 is multiplied with the output from logarithmic amplifier 120 by a multiplier 127 which provides a signal to antilog circuit 125A. Circuit 125A provides a signal to subtracting means 128 which subtracts a direct current voltage C₁ from the signal from circuit 125A to provide signal E₅.

Referring now to FIG. 7, VI signal means 63 is essentially memory means which is addressed by signals E₅, corresponding to KV₁₀₀, and signal KV₂₁₀. In this regard, a comparator 130 and comparator 130A represent a plurality of comparators which receive signal E₅ and compare signal E₅ to reference voltages, represented by voltages R₁ and R₂, so as to decode signal E₅. Similarly, comparators 130B and 130C represent a plurality of comparators receiving signal KV₂₁₀ which compare signal KV₂₁₀ with reference voltages RA and RB so as to decode signal KV₂₁₀. The outputs from comparators 130 and 130B are applied to an AND gate 133 whose output controls a switch 135. Thus, should comparators 130 and 130B provide a high output, AND gate 133 is enabled and causes switch 135 to be rendered conductive to pass a direct current voltage V_(A) corresponding to a predetermined value, as signal E₆ which corresponds to VI. Similarly, the outputs of comparators 130 and 130C control an AND gate 133A which in turn controls a switch 135A to pass or to block a direct current voltage V_(B). Similarly, another AND gate 133B is controlled by the outputs from comparators 130A and 133B is controlled by the outputs from comparators 130A and 130B to control a switch 135B so as to pass or block a direct current voltage V_(C). Again, an AND gate 133C is controlled by the outputs from comparators 130A and 130C to control a switch 135C to pass or to block a direct current voltage V_(D). The outputs of switches 135 through 135C are tied together so as to provide a common output.

Referring now to FIG. 8, the SUS computer 65 includes multipliers 136, 137 and 138 multiplying signal KV₂₁₀ with direct current voltages C₉, C₇ and C₅, respectively, to provide signals corresponding to the terms C₉ (KV₂₁₀), C₇ (KV₂₁₀) and C₅ (KV₂₁₀), respectively in equation 6. A multiplier 139 effectively squares signal KV₂₁₀ to provide a signal to multipliers 140 141. Multiplier 140 multiplies the signal from multiplier 139 with a direct current voltage C₁₀ to provide a signal corresponding to the term C₁₀ (KV₂₁₀)² in equation 6. Multiplier 141 multiplies the signal from multiplier 139 with signal KV₂₁₀ to provide a signal corresponding to (KV₂₁₀)³. A multiplier 142 multiplies the signal from multiplier 141 with a direct current voltage C₁₁ to provide a signal corresponding to the term C₁₁ (KV₂₁₀)³ in equation 6. Summing means 143 sums the signals from multipliers 136, 140 and 142 with a direct current voltage C₈ to provide a signal to a multiplier 144 where it is multiplied with a direct current voltage C₁₂. The signal from multiplier 137 is summed with a direct current voltage C₆ by summing means 145 to provide a signal corresponding to the term [C₆ +C₇ (KV₂₁₀)]. A divider 146 divide the signal provided by summing means 145 with the signal provided by multiplier 144 to provide a signal which is summed with the signal from multiplier 138 by summing means 147 to provide signal E₇.

Referring now to FIG. 9, SUS₂₁₀ computer 68 includes subtracting means 148 which subtracts a direct current voltage C₁₆ from another direct current voltage C₁₆ from another direct current voltage C₁₅ to provide a signal corresponding to the term (C₁₅ -C₁₆) in equation 7. The signal from subtracting means 148 is multiplied with a direct current voltage C₁₄ by a multiplier 149 to provide a product signal which is summed with another direct current voltage C₁₃ by summing means 150. Summing means 150 provides a signal corresponding to the term [C₁₃ +C₁₄ (C₁₅ -C₁₆ ] in equation 7. The signal from summing means 150 is multiplied with signal E₇ by a multiplier 152 to provide signal E₈.

Referring now to FIG. 10, there is shown W computer 69 having multipliers 155, 156 and 157 receiving signal API. Multiplier 155 multiplies signal API with signal S to provide a product signal to another multiplier 160 where it is multiplied with a direct current voltage C₄₉ to provide a signal corresponding to the term C₄₉ (S) (API) in equation 8. Multiplier 156 effectively squares signal API and provides a signal to another multiplier 163 where it is multiplied with a direct current voltage C₄₇ to provide a signal corresponding to the term (C₄₇) (API)². Multiplier 157 multiplies signal API with a direct current voltage C₄₄ to provide a signal corresponding to the term C₄₄ (API). A divider 166 divides signal API with signal KV₂₁₀ to provide another signal to a multiplier 168 where it is multiplied with a direct current voltage C₄₈ which in turn provides a signal corresponding to the term [C₄₈ (API)/(KV₂₁₀)] in equation 8. A divider 170 divides a direct current voltage C₄₅ with signal KV₂₁₀ to provide a signal corresponding to the term C₄₅ /(KV₂₁₀). A multiplier 173 multiplies signal S with a direct current voltage C₄₆. Summing means 175 sums a direct current voltage C₄₃ with the signals provided by multipliers 160, 163 and divider 170. Other summing means 176 sums the signals provided by multipliers 157, 168 and 173. Subtracting means 179 subtracts the signal provided by summing means 176 from the signal provided by summing means 175 to provide signal E₉.

Referring now to FIG. 11, VI_(DWC).sbsb.O computer 70 includes a multiplier 180 receiving signals E₆, E₉ and providing a product signal to another multiplier 182 where it is multiplied with a direct current voltage C₅₄ Multiplier 182 provides a signal corresponding to the term C₅₄ (W) (VI) in equation 9. Another multiplier 185 multiplies signal RI with a direct current voltage C₅₁ to provide a signal corresponding to the term (C₅₁) (RI). Summing means 188 sums the signals from multipliers 182, 185.

A multiplier 190 multiplies signals E₆ and RI to provide a product signal to another multiplier 193 where it is multiplied with a direct current voltage C₅₂. Multiplier 193 provides a product signal to summing means 198. Another multiplier 200 multiplies signals FL and API to provide a product signal to a multiplier 202 where it is multiplied with a direct current voltage C₅₃. Multiplier 322 provides a signal corresponding to the term C₅₃ (FL) (API) in equation 9 to summing means 198 where it is summed with the signal from multiplier 315 and a direct current voltage C₅₀ to provide a sum signal. Subtracting means 205 subtracts the sum signal provided by summing means 188 from the signal provided by summing means 198 to provide signal E₁₀.

VI_(DWC).sbsb.P computer 72 shown in FIG. 12, includes a natural logarithm function generator 200 receiving signal E₈ and providing a signal corresponding to the term lnSUS₂₁₀ to multipliers 201 and 202. Multiplier 201 multiplies the signal from function generator 200 with a direct current voltage C₂₂ to provide a signal corresponding to the term C₂₂ ln SUS₂₁₀ in equation 10. Multiplier 202 effectively squares the signal from function generator 200 to provide a signal that is multiplied with the direct current voltage C₂₃ by a multiplier 205. Multiplier 205 provides a signal corresponding to the term C₂₃ (ln SUS₂₁₀)² in equation 10. Subtracting means 206 subtracts the signals provided by multiplier 201 from the signal provided by multiplier 205. Summing means 207 sums the signal from subtracting means 206 with a direct current voltage C₂₁. A multiplier 208 multiplies the sum signals from summing means 207 with a direct current voltage POUR to provide a signal which is summed with signal E₉ by summing means 210 which provides signal E₁₁.

Referring now to FIG. 13, A computer 79 includes a multiplier 212 multiplying signal API with a direct current voltage C₅₆ to provide a signal corresponding to the term C₅₆ (API) in equation 12. Another multiplier 213 multiplies signals FL and KV₂₁₀ to provide a product signal to a multiplier 215 where it is multiplied with a direct current voltage C₅₇. Multiplier 215 provides a product signal corresponding to the term C₅₇ (FL) (KV₂₁₀) in equation 12 to summing means 218. Summing means 218 sums the signal provided by multiplier 215 with a direct current voltage C₅₅ to provide a sum signal. Subtracting means 220 subtracts the signal provided by multiplier 212 from the sum signal provided by summing means 218 to provide signal A.

Referring now to FIG. 14, J computer 80 includes multipliers 225 and 226 multiplying signal A with direct current voltages C₅₈ and C₅₉ respectively. Multiplier 228 effectively squares the signal provided by multiplier 225 to provide a signal corresponding to the term (C₅₈ A)² to subtracting means 234. Multiplier 235 multiplies the signal from multiplier 226 with a direct current voltage V₄ corresponding to a value of 4 to provide a product signal to another multiplier 236.

A square root circuit 240 receives signal T and provides a signal corresponding to (T)^(1/2) to a multiplier 243 where it is multiplied with a direct current voltage C₆₁. Multiplier 243 provides a product signal to subtracting means 247 where signal E₁₂ corresponding to ΔVI is subtracted from it to provide a difference signal. Summing means 250 sums the difference signal from subtracting means 367 with direct current voltage C₆₀ to provide a signal corresponding to the term [C₆₀ +C₆₁ (T)^(1/2) -ΔVI] in equation 13 to multiplier 236. Multiplier 236 multiplies the signal provided by multiplier 235 with the signal provided by summing means 250 to provide a signal to subtracting means 234 where it is subtracted from the signal provided by multiplier 228. Subtracting means 234 provides a difference signal to a square root circuit 256 which provides a signal to subtracting means 260. Subtracting means 260 subtracts the signal provided by multiplier 225 from the signal provided by square root circuit 256 to provide a signal to a divider 263. A multiplier 265 multiplies a direct current voltage V₂₃, corresponding to a value of 2, with the signal provided by multiplier 226 to provide a product signal to divider 263 where it is divided into the signal provided by subtracting means 260. Divider 383 provides signal E₁₃.

The present invention is hereinbefore described controls a furfural refining unit receiving medium sweet charge oil to achieve a desired charge oil flow rate for a constant furfural flow rate. It is also within the scope of the present invention, as hereinbefore described, to control the furfural flow rate while the medium sweet charge oil flow is maintained at a constant rate. 

The claim:
 1. A control system for a furfural refining unit receiving medium sweet charge oil and furfural, one of which is maintained at a fixed flow rate while the flow rate of the other is controlled by the control system, treats the received charge oil with the received furfural to yield extract mix and raffinate, comprising gravity analyzer means for sampling the medium sweet charge oil and providing a signal API corresponding to the API gravity of the medium sweet charge oil, flash point analyzer means for sampling the medium sweet charge oil and providing a signal FL corresponding to the flash point temperature of the charge oil, viscosity analyzer means for sampling the medium sweet charge oil and providing signals KV₁₅₀ and KV₂₁₀ corresponding to the kinematic viscosities, corrected to 150° F. and 210° F., respectively, sulfur analyzer means for sampling the medium sweet charge oil and providing a signal S corresponding to the sulfur content of the medium sweet charge oil, a refractometer samples the medium sweet charge oil and provides a signal RI corresponding to the refractive index of the medium sweet charge oil, flow rate sensing means for sensing the flow rates of the medium sweet charge oil and of the furfural and providing signals CHG and SOLV, corresponding to the medium sweet charge oil flow rate and the furfural flow rate, respectively, means for sensing the temperature of the extract mix and providing a corresponding signal T, and control means connected to all of the analyzer means, the refractometer, and to all the sensing means for controlling the other flow rate of the charge oil and the furfural flow rates in accordance with signals API, FL, KV₁₅₀, S, RI, CHG, T and SOLV.
 2. A system as described in claim 1, in which the control means includes VI signal means connected to the viscosity analyzer means for providing a signal VI corresponding to the viscosity index of the medium sweet charge oil in accordance with viscosity signals KV₁₅₀ and KV₂₁₀ ; SUS₂₁₀ signal means connected to the viscosity analyzer means for providing a signal SUS₂₁₀ corresponding to the medium sweet charge oil viscosity in Saybolt Universal Seconds corrected to 210° F.; W signal means connected to the viscosity analyzer means, to the gravity analyzer means and to the sulfur analyzer means for providing a signal W corresponding to the wax content of the medium sweet charge oil in accordance with signals KV₂₁₀, API and S; A signal means connected to the viscosity analyzer means, to the gravity analyzer means and to the flash point temperature analyzer means for providing a signal A corresponding to an interim factor A in accordance with signals KV₂₁₀, API and FL; ΔVI signal means connected to the gravity analyzer means, to the flash point temperature analyzer means, to the refractometer, to the VI signal means, to the W signal means and to the SUS₂₁₀ signal means and receiving voltage VI_(RP) for providing a signal ΔVI corresponding to the change in viscosity index in accordance with signals VI, W, API, FL, RI, SUS₂₁₀ and voltage VI_(RP) ; J signal means connected to the ΔVI signal means, to the A signal means, and to the temperature sensing means for providing a J signal corresponding to the furfural dosage for medium sweet charge oil in accordance with the signals ΔVI, A and T; control signal means connected to the J signal means and to the flow rate sensing means for providing a control signal in accordance with the J signal and one of the sensed flow rate signals, and apparatus means connected to the control network means for controlling the one flow rate of the medium sweet charge oil and furfural flow rates in accordance with the control signal.
 3. A system as described in claim 2 in which the SUS₂₁₀ signal means includes SUS signal means connected to the viscosity analyzer means, and receiving direct current voltages C₅ through C₁₂ for providing a signal SUS corresponding to an interim factor SUS in accordance with signal KV₂₁₀, voltages C₅ through C₁₂ and the following equation:

    SUS=C.sub.5 (KV.sub.210)+[C.sub.6 +C.sub.7 (KV.sub.210)]/[C.sub.8 +C.sub.9 (KV.sub.210)+C.sub.10 (KV.sub.210).sup.2 +C.sub.11 (KV.sub.210).sup.3 ](C.sub.12),

where C₅ through C₁₂ are constants; and SUS₂₁₀ network means connected to the SUS signal means and to the ΔVI signal means and receiving direct current voltages C₁₃ through C₁₆ dor providing signal SUS₂₁₀ to the ΔVI signal means in accordance with signal SUS, voltages C₁₃ through C₁₆ and the following equation:

    SUS.sub.210 =[C.sub.13 +C.sub.14 (C.sub.15 -C.sub.16)]SUS,

where C₁₃ through C₁₆ are constants.
 4. A system as described in claim 3 in which the W signal means further receives direct current voltages C₄₃ through C₄₉ and provides signal W in accordance with signals API, KV₂₁₀ and S, voltages C₄₃ through C₄₉, and the following equation:

    W=C.sub.43 -C.sub.44 API+C.sub.45 /KV.sub.210 -C.sub.46 S+C.sub.47 (API).sup.2 -C.sub.48 API/KV.sub.210 +C.sub.49 (S) (API),

where C₄₃ through C₄₉ are constants.
 5. A system as described in claim 4 in which the VI signal means includes K signal means receiving direct current voltages C₂, C₃, C₄ and T₁₅₀ for providing a signal K₁₅₀ corresponding to the kinematic viscosity of the charge oil corrected to 150° F. in accordance with voltages C₂, C₃, C₄ and T₁₅₀, and the following equation:

    K.sub.150 =C.sub.2 -[ln(T.sub.150 +C.sub.3)]/C.sub.4,

where C₂ through C₄ are constants, and T₁₅₀ corresponds to a temperature of 150° F.; H₁₅₀ signal means connected to the viscosity analyzer means and receiving a direct current voltage C₁ for providing a signal H₁₅₀ corresponding to a viscosity H value for 150° F. in accordance with signal KV₁₅₀ and voltage C₁ in the following equation:

    H.sub.150 =lnln(KV.sub.150 +C.sub.1),

where C₁ is a constant; H₂₁₀ signal means connected to the viscosity analyzer means and receiving voltage C₁ for providing signal H₂₁₀ corresponding to a viscosity H value for 210° F. in accordance with signal KV₂₁₀, voltage C₁ and the following equation:

    H.sub.210 =lnln(KV.sub.210 +C.sub.1),

H₁₀₀ signal means connected to the K signal means, to the H₁₅₀ signal means and the H₂₁₀ signal means for providing a signal H₁₀₀ corresponding to a viscosity H value for 100° F., in accordance with signals H₁₅₀, H₂₁₀ and K₁₅₀ and the following equation:

    H.sub.100 =H.sub.210 +(H.sub.150 -H.sub.210)/K.sub.150

Kv₁₀₀ signal means connected to the H₁₀₀ signal means and receiving voltage C₁ for providing a signal KV₁₀₀ corresponding to a kinematic viscosity for the charge oil corrected to 100° F. in accordance with signal H₁₀₀, voltage C₁, and the following equation:

    KV.sub.100 =exp[exp(H.sub.100)]-C.sub.1,

and VI memory means connected to the KV₁₀₀ signal means and to the viscosity analyzer means having a plurality of signals stored therein, corresponding to different viscosity indexes and controlled by signals KV₁₀₀ and KV₂₁₀ to select a stored signal and providing the selected stored signal as signal VI.
 6. A system as described in claim 5 in which the A signal means also receives direct current voltages C₅₅ through C₅₆ and provides A signal in accordance with signals API, FL and KV₂₁₀, voltages C₅₅ through C₅₇ and the following equation:

    A=C.sub.55 -C.sub.56 (API)+C.sub.57 (FL) (KV.sub.210),

where C₅₅ through C₅₇ are constants.
 7. A system as described in claim 6 in which the ΔVI signal means includes a VI_(DWC).sbsb.O signal means connected to the gravity analyzer means, the flash point temperature analyzer means, the refractometer, the VI signal means and the W signal means, and receives direct current voltages C₅₀ through C₅₄ and provides a VI_(DWC).sbsb.O signal in accordance with signals RI, VI, FL, W and API, voltages C₅₀ through C₅₄ and the following equation:

    VI.sub.DWC.sbsb.O =C.sub.50 -C.sub.51 RI+C.sub.52 (RI) (VI)+C.sub.53 (FL) (API)-C.sub.54 (W) (VI),

where C₅₀ through C₅₄ are constants, a VI_(DWC).sbsb.P signal means and to the SUS₂₁₀ signal means for providing a VI_(DWC).sbsb.P signal in accordance with signals SUS₂₁₀ and VI_(DWC).sbsb.O, voltages C₂₁ through C₂₃ and Pour, and the following equation:

    VI.sub.DWC.sbsb.P =VI.sub.DWC.sbsb.O +(POUR)[C.sub.21 -C.sub.22 lnSUS.sub.210 +C.sub.23 (lnSUS.sub.210).sup.2 ],

and subtracting means connected to the J signal means and to the VI_(DWC).sbsb.P signal means and receiving voltage VI_(RP) for subtracting signal VI_(DWC).sbsb.P from voltage VI_(RP) to provide the ΔVI signal to the J signal means.
 8. A control system as described in claim 7 in which the J signal means receives direct current voltages C₅₈ through C₆₁ and provides the J signal in accordance with the received voltages C₅₈ through C₆₁, signals A, T and ΔVI and the following equation:

    J={{-C.sub.58 A+{(C.sub.58 A).sup.2 -4C.sub.59 A(C.sub.60 +C.sub.61 √T-ΔVI)}.sup.1/2 }/2C.sub.59 A}.sup.2,

where C₅₈ through C₆₁ are constants.
 9. A system as described in claim 8 in which flow rate of the medium sweet charge oil is controlled and the flow of the furfural is maintained at a constant rate and the control signal means receives signal SOLV from the flow rate sensing means, the J signal from the J signal means and a direct current voltage corresponding to a value of 100 and provides a signal C to the apparatus means corresponding to a new medium sweet charge oil flow rate in accordance with the J signal, signal SOLV and the received voltage and the following equation:

    C=(SOLV) (100)/J,

so as to cause the apparatus means to change the charge oil flow to the new flow rate.
 10. A system as described in claim 8 in which the controlled flow rate is the furfural flow rate and the flow of the medium sweet charge oil is maintained constant, and the control signal means is connected to the sensing means, to the selection means and receives a direct current voltage corresponding to the value of 100 for providing a signal SO corresponding to a new furfural flow rate in accordance with signals CHG, J and the received voltage, and the following equation:

    SO=(CHG) (J)/100,

so as to cause the furfural flow to change to the new flow rate. 